This is effectively implements "animationWorklet.registerAnimator" function in animation worklet global scope.

- Validate all the expected static getter values (e.g., inputProperties, inputChildProperties, inputTime, etc...) and throw appropriate errors
- Validate there is a constructor and an animate function
- Create an object to encapsulate the parsed V8 functions (AnimatorDefinition)
- Create a map in worklet scope for name -> AnimatorDefinition

These definition objects will be used when we see an animator assignment in CSS and decide to create/initialize a new animator instance.